The present invention relates generally to a filter apparatus, and more particularly to a filter apparatus having substantially horizontal filter elements of plate-like configuration which are rotatable about an upright axis in order to centrifugally discharge filtered-out residue that has accumulated on them.
Filter apparatus of this type is known per se, for instance from my U.S. Pat. No. 3,251,468 and from my Swiss Pat. No. 369,747. This type of filter apparatus usually uses for each filter element an imperforate plate member which projects transversely of an upright rotatable shaft which is hollow, and a filter cloth overlying the upwardly facing side of the plate member. The liquid then filters through the filter cloth and runs beneath the same on the surface of the plate member towards the shaft, for which purpose the plate member is slightly dished so as to be inclined inwardly towards the shaft. The shaft itself is provided with perforations through which the liquid then can run into the interior of the shaft, which is hollow and from where the liquid runs off for further use. The filtered-out residue forms a filter cake on the surface of the filter cloth, and when the cake formation has progressed to a certain extent, for instance to the empirically determined point at which filtration is no longer adequate because of clogging of the filter cloth, filtration is stopped and the shaft and filter elements which heretofore have been stationary, are rotated at relatively high speed so that the filter cake is flung off the surface of the filter cloths under the influence of centrifugal force.
Subsequent to the centrifugal ejection of the filter cake, the filter elements are subjected to a back-flushing operation, in that liquid for cleaning purposes is made to pass through the filter elements, or rather particularly through the filter cloths, while the rotation still continues, so as to remove any residual filtered-out matter from the cloth.
During this back-flushing operation the filter cloth exhibits a tendency to move off the underlying plate member of the filter element; this can lead to damage to the filter cloth or at the very least to deformations in the filter cloth which during the nextfollowing filtering cycle will disadvantageously influence the filtering capability. It is known for this reason to provide on a spacer ring which surrounds the shaft intermediate the adjacent filter elements, a plurality of rod-shaped fingers or projections which extend outwardly from the spacer ring and are intended to hold the filter cloth down against the associated plate member. However, experience has shown that in many circumstances, particularly if the filtered-out matter tends to cling to the filter cloth, a deformation of these rod-shaped fingers takes place, causing the same to bend irreversibly so that they no longer hold the filter cloth properly against the plate member during the back-flushing operation and subsequently during the next-following filtering operation.